I remember reading an article once, before Batman Begins was ever released, on the theory of a real superhero.

Conceptually, the pitch was that if the hero is like Batman, a human being and not endowed with super powers, then the closest approach to how his career would or could go would be by comparing it to an all-star athlete. The guy wouldn't be able to last 30 years or anything, because eventually the bumps and bruises would build up. So either he'd catch a bullet or just not be able to get up in the morning. And the idea would also be that there'd be a peak, where he would be an absolute beast. He'd be at peak physical condition, very confident and sure of himself, and be completely healthy. In his prime, around his early 30's. And then it'd just kinda go downhill after that.

I think Nolan's films, more or less, kinda followed that type of trajectory. Bruce became Batman was pretty much leaped into it in his prime. He was probably Batman for about 3 or 4 years. But, I guess he got a ton done. Aside from Bane, Ra's, Scarecrow, and the Joker...who all had a hand in major plans, Batman's biggest opponent in Gotham was organized crime. With the Dent Act getting passed, probably a few years after Dent died, that was it for organized crime in Gotham.

The film did seem to emphasize that Bruce was not exactly forced into retirement by his injury. His injury wasn't really holding him back. The first whiff of anything big had him ready to roll. He retired because he and Jim had won. He definitely got usage out of the Batcave, which I assume wasn't ready during TDK since it hadn't been seen.